JTAG Problems

OK, I updated my JTAG xbox with donor files as my NAND was playing up and now it will turn on but not display anything. I can turn it on with the controller and sync with it but that's about it. It will also not boot into Xellous. Any help is much appreciated.

Thanks for the help Jpizzle, you're great. Sigh, I can't be bothered fixing this though as I barely play it anymore. Might fix it later down the track or just end up selling it. Thanks for the help anyway.